Fig. 5 shows the monotonic and cyclic stress-strain responses of selected specimens having all influential parameters considered in this study, such as the volumetric ratio of transverse steel reinforcement, number of CFRP layers, and aspect ratio. In this figure, the axial stress was calculated by dividing the axial load to the column cross-sectional area, and the corresponding axial strain was derived from the average readings of the four LVDTs divided by the central gauge length of each column. The hoop rupture strain was calculated as average value resulted from all CFRP mounted strain gauges without considering the ones located at the overlap zone. Table 1 presents the summary of the experimental results of all specimens tested in this
…show more content…
5, the axial stress-strain relationships of CFRP-confined rectangular columns of large-size can be characterized by a three-stage response known as post-peak softening behavior followed by an increase in the stress. Such behavior is directly related to the confinement effectiveness by CFRP layers and hoops reinforcement, which decreases with an increase in the geometric dimensions of concrete column. The resulted behavior is believed to be much degraded beyond the peak point due to dilation in concrete when using inadequate amount of confinement material (Harries and Kharel 2003). After the peak load was reached, the decrease in axial strength was more remarkable for larger dimensioned specimens. For instance, the axial stress decreased suddenly by 14% and 41.8% for specimens R1.5H2CL3 and R2.0H2CL3, respectively, comprising softening region as a second portion of the overall behavior of these columns. Similar post peak softening behavior followed by an increase in stress was also found in several studies (e.g., Yan 2005; Rocca 2007; Youssef et al. 2007; Wang et al. 2012a). The following sections of this paper include a detailed discussion for this phenomenon. Fig. 5 also shows that the envelope curves of cyclically loaded columns approximately follow their monotonic stress-strain curves. A similar phenomenon has also found in test results of FRP-confined concrete columns subjected to monotonic and cyclic compression loads (e.g., Ilki et al. 2008; Abbasnia and Ziaadiny 2010; Ozbakkaloglu and Akin 2012; Wang et al. 2012a; Hany et al.
5, the axial stress-strain relationships of CFRP-confined rectangular columns of large-size can be characterized by a three-stage response known as post-peak softening behavior followed by an increase in the stress. Such behavior is directly related to the confinement effectiveness by CFRP layers and hoops reinforcement, which decreases with an increase in the geometric dimensions of concrete column. The resulted behavior is believed to be much degraded beyond the peak point due to dilation in concrete when using inadequate amount of confinement material (Harries and Kharel 2003). After the peak load was reached, the decrease in axial strength was more remarkable for larger dimensioned specimens. For instance, the axial stress decreased suddenly by 14% and 41.8% for specimens R1.5H2CL3 and R2.0H2CL3, respectively, comprising softening region as a second portion of the overall behavior of these columns. Similar post peak softening behavior followed by an increase in stress was also found in several studies (e.g., Yan 2005; Rocca 2007; Youssef et al. 2007; Wang et al. 2012a). The following sections of this paper include a detailed discussion for this phenomenon. Fig. 5 also shows that the envelope curves of cyclically loaded columns approximately follow their monotonic stress-strain curves. A similar phenomenon has also found in test results of FRP-confined concrete columns subjected to monotonic and cyclic compression loads (e.g., Ilki et al. 2008; Abbasnia and Ziaadiny 2010; Ozbakkaloglu and Akin 2012; Wang et al. 2012a; Hany et al.